1. Field of the Invention
This invention relates to a method and apparatus for forming a container which has a body that is fabricated from a sheet of a thermoplastic material and to a container which is fabricated thereby. More particularly this invention relates to a method and apparatus for forming a container of the foregoing description which has a rolled rim at the mouth thereof and a substantially uniform thickness in the sidewall thereof, and to a container of such description. This invention also relates to a method and apparatus for forming a container of the foregoing description whose bottom has a thin, annular bearing ring surrounding a raised central portion for improved stability on a flat surface, and to a container of such description.
2. Description of the Prior Art
U.S. Pat. No. 3,854,583 (Amberg et al.) discloses a container that includes a body which is fabricated from a sheet of an expanded thermoplastic material and which is provided with a rolled rim or bead at the mouth of such container. Such rolled rim or bead helps to stiffen the container at the mouth thereof, it provides a smooth edge for drinking a beverage from the container, and it provides a protrusion from the sidewall of the container that is useful in securing a cap or closure to the container. Containers of the type illustrated in the aforesaid U.S. Pat. No. 3,854,583 have a generally vertically extending side seam where the wall thickness is approximately double the thickness of the original sheet, due to the fact that it is formed by overlapping the leading and trailing edges of the sheet. Such containers have been extensively utilized as cups for single service quantities of a beverage, for example, coffee, and, when so utilized, the bodies of such containers have typically been manufactured in a nestable or frustoconical configuration from rectangular blanks of a heat-shrinkable thermoplastic material by a process which includes the shrinking of a cylindrical sleeve formed from such blank against the outer surface of a frustoconical forming mandrel. Because of the thickness of the side seams of containers of this type, they are not sufficiently close-nesting, and they are not sufficiently mechanically denestable, to permit their use in vending machines. Further, cups or containers of the foregoing description have bottoms with annular bearing surfaces which are rather wide, in a radial direction, and which are, therefore, subject to being formed in a somewhat non-planar condition. Consequently, such cups need to be fairly wide in relation to their height, to be sufficiently resistant to accidental tipping even when placed on a flat, horizontal surface. Typically, cups of the foregoing character have been produced by apparatus similar to that disclosed in U.S. Pat. No. 4,053,346 (Amberg et al.), and may also be produced by apparatus similar to that disclosed in U.S. Pat. No. 4,072,549 (Amberg et al.).
In the manufacture of cups of the type described in the aforesaid U.S. Pat. No. 3,854,583, either by apparatus of the type described in the aforesaid U.S. Pat. No. 4,053,346 or by the apparatus of the type described in the aforesaid U.S. Pat. No. 4,072,549, heretofore it has been necessary to effect rotation of the cup relative to the rim-forming tooling of the apparatus during the rolling of the rim in the body of the cup to obtain a properly formed and rolled rim. As is clear from each of the aforesaid U.S. Pat. Nos. 4,053,346 and 4,072,549, it is necessary to provide rather complex apparatus to effect such relative rotation between each of the cups and the rim-forming tooling that is used to roll rims in such cups, and the complexity of such apparatus adds to the initial expense in manufacturing such apparatus and to subsequent expenses related to its maintenance and operation. Further, apparatus of the foregoing character has not incorporated structure to reduce the thickness of the vertical seam in the body of the cups. Thus, cups produced by such apparatus have had thick seams and it has not been feasible to use such cups in vending machines. Further, cups produced by such apparatus have had annular bearing surfaces which are rather thick, in a radial direction, a condition which can lead to an out-of-flat or non-planar bottom bearing surface. Thus, it was necessary for such cups to be relatively wide in relation to their height to be sufficiently resistant to accidental tipping.